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Smoke is discharged from chimneys at a plant in Tokyo, Tuesday, March 25.Eugene Hoshiko/The Associated Press

For Debra Davidson, the most immediate impact of global climate change has been on her sleep cycle this week.

Dr. Davidson, a sociologist at the University of Alberta, is one of about 50 researchers participating in a series of marathon sessions to hammer out the final wording of a UN document on the effects of climate change.

"It's our last official day and we still have a lot to cover, so I fear tonight will be an all-nighter," Dr. Davidson said, speaking early Saturday morning from Yokohama, Japan, where the Intergovernmental Panel on Climate Change (IPCC) has been meeting for the past four days.

The aim of the meeting is producing a definitive summary for policy makers, reflecting key takeaway messages from an encyclopedic, 30-chapter scientific review that details the ways in which climate change is already making itself apparent around the globe, as well as the more profound impacts that are anticipated over the course of the century.

The report forms the second part of the IPCC's latest assessment of the state of the world's knowledge on climate change, the first since 2007. An earlier part, released last fall, dealt with the physical evidence for climate change and pegged the likelihood that humans are causing it at the 95-per-cent confidence level. A third and final part, due to be released in mid-April, deals with mitigating the effects by reducing greenhouse-gas emissions.

But it is this second part, scheduled for release at a media briefing in Japan on Monday morning (Sunday evening in Canada), that is expected to paint the most vivid picture to date of how climate change is influencing the planet, particularly in sectors that have high economic impact, including freshwater resources, agriculture, forestry, fisheries and threats to wildlife and biodiversity.

"Now we're starting to see a lot more specificity, in terms of the impacts that have unfolded to date, how they will unfold in future, with what certainty and to what extent we can attribute it to global climate change," said Kelly Levin, a climate policy specialist and senior associate with the World Resources Institute based in Washington.

While there remains little doubt in the scientific community that climate change is already having a significant effect on both natural and human systems, the question is how forcefully this will be worded in the IPCC summary, which must past muster in a line-by-line reading by delegates from participating governments including Canada.

Dr. Levin said she expected the language of the report to reflect a shift from talking about the "discernible influence" of climate change, as described in the previous assessment, to discussing effects that are both "widespread and consequential."

The increase in detail and confidence is a function of how much more information the scientific community has to work with since the last time it went through this process, said Mike Brklacich, a professor of geography and environmental studies at Carleton University in Ottawa and a lead author on the chapter dealing with emergent risks due to climate change.

"The body of knowledge that's available worldwide now is much larger than it was [in 2007]," he said.

It also includes new dimensions, such as the impact of climate change on human security. This is an area the IPCC did not consider in previous assessments, but that will be amply reflected in the new report, Prof. Brklacich added.

Another way the report is said to differ from previous efforts is by putting more emphasis on the rate at which the climate is changing, rather than just the magnitude of the change. This will dictate how quickly governments and people must adapt to a level of global warming that is effectively guaranteed by the carbon that has already been released into the atmosphere.

Yet, according to most scenarios, the scale of the impact by the end of the century is likely to be so large that adaptation strategies alone won't be sufficient. This implies that meeting emission-reduction targets are still essential in parallel with adaptation to avert the greatest risks from climate change.

"There's no room for complacency here," Dr. Davidson said. "But I think there's a lot of room for rolling up our sleeves and getting to work because there's a lot that we can do."